When you visit a site PhishTank has verified as an active phish, the SiteChecker extension blocks the site, giving you the option to go back, continue safely to the site for a limited time, or view details of the dirty site on PhishTank. If you know anyone who's particularly susceptible to phishing scams (surely you can spot a phishing site a mile away), this Firefox extension could prove invaluable. PhishTank SiteChecker is a free download, works wherever you're running the 'fox. — Adam Pash